"Locked Diff Welded" - Meaning?

[revilla]

Saw this Sierra differential on eBay and the description included the phrase "locked diff welded". Not understanding what was meant by this I messaged the seller to ask if it had been repaired. The response I got was:

 

"no it hasnt had any repairs what the lock diff welded means is in side the diff one of the gears inside gets welded up to lock it off so say when you go around the corner one wheel lifts up the unlock starts making the one lifting to spin after and the one on the floor to slow down but a lock diff stop the one on the floor from slowing down and keeps it to the normal speed that you are doing. dont know if that helps hard to ecplain it 

thanks"

 

Is he actually saying that the diff has been welded up internally such that it no longer allows any differential movement at all? So instead of for example a limited-slip diff this has been converted into a no-slip diff? Why on earth would anyone want to do that, wouldn't it just induce massive understeer and eat the rear tyres? Or am I missing something?

[6speedmanual]

Yes, it is as you and seller describe.

Usually for dirt or grass track racing where the car is a lot sideways with high rear wheel slip induced oversteer.

Not useful in grippy conditions as you already deduced.

 

P

[revilla]

Ah I see. Thank you.

[Scott Dabinett]

It most prob came from a drift car! It is the norm in drifting to weld the diff so both wheels spin at the same time. It is a lot more predictable than an LSD(and cheaper) when drifting because it won't come unlocked but makes the car awful to drive at anything below 20mph.

 

Edited by - Scott Dabinett on 3 Apr 2014 07:15:56

[Mankee]

Welded diffs always make me think of old Volvo 240s/340s/360s/740s/760s going tramp drifting.

 

http://doristars.com/v-web/gallery/albums/duk09-11/DSC_0119.sized.jpg

[SLR No.77]

Stockcar racers do it .... Paul Richards is your man to explain it all 😬

 

Stu.

[shn7]

Drove a Sierra with this at the Essex Police dkid pan. Certainly makes for tail happy fun.

[Dave Rayner]

My old autrograss Escort had a welded diff, great fun driving looking out the side window when going straight!!!

[revilla]

Well I have to say that I'd never heard about it before, but clearly a lot of other people have. There's something new to learn on BlatChat every day! Thanks for all the info, always interesting to broaden one's education even though it doesn't sound like something that should go anywhere near my Seven. Now I'm just trying to imagine what surprises I would have let myself in for if I had fitted it 😬

[Slipper man]

Not sure what they do now, but in the 1970's (e.g. types 908, 917), Porsche used locked diffs on all their race cars. IIRC, it was lighter, more robust and on a circuit made very little difference in their tests

[tony pashley]

Some of the 935s were using a 'solid' diff into the late 70s at least - esp in the German Group 5 series; I think some of their tracks were quicker than the UK (or US) ones, which maybe made a difference. When that series came to the UK in the late 70s (ah, happy memories), Guy Edwards, whose 935 (or maybe a Kremer K3?) was thus equipped, said his car felt 'muscle-bound' around Donington - and the Porsches were utterly trounced by Zakspeed's much smaller-engined Capri - which I believe used a more 'usual' lsd.

 

A locked diff always sounds like hard work on a road course to me, but I've never driven one.

[Guest]

One could do like we did with 4X4's. ARB air lock diff. Full locking to open diff with the flick of a switch.

linky

 

 

Edited by - bigdog on 3 Apr 2014 13:03:09

[andy couchman]

I thought Porsche 956/962 were running locked diffs into the 90s too?

 

Might it have helped with keeping the cars straight down the Hunaudieres straight at 240mph? Made it tricky for the mechanics to manoeuvre in park fermé though.

 

Andy

[tony pashley]

That does sound familiar, Andy. I'd forgotten about the 'modern' stuff!

 

Mark Donohue favoured a locked diff (a 'spool'?) (well. I suppose that's 'no diff' really) - they even had one on that georgeous Penske Ferrari 512. He talks of diffs quite a bit in his book 'The unfair advantage'. He must have found value in them to fit them to cars which didn't have then as designed. I think he wrote of it allowing him to make much better use of the brakes in some way - I forget the details. Difficult to argue with Donohue though...

 

I believe some "Aussie V8" touring cars use them too.

 

While we're on the subject, I've never been wholly clear on what a 'Detroit Locker' is; my understanding was that it's neither fully solid or open, nor fully lsd, but switches between open and locked, with no progression. Anyone know if that's correct?

 

Edited by - tony pashley on 3 Apr 2014 13:42:06

[Jonathan Kay]

Automatic lockers, from Wikipedia:

Automatic lockers lock and unlock automatically with no direct input from the driver. Some automatic locking differential designs ensure that engine power is always transmitted to both wheels, regardless of traction conditions, and will "unlock" only when one wheel is required to spin faster than the other during cornering. These would be more correctly termed "automatic unlocking" differentials, since their at-rest position is locked. They will never allow either wheel to spin slower than the differential carrier or axle as a whole, but will permit a wheel to be over-driven faster than the carrier speed. The most common example of this type would be the famous "Detroit Locker," also known as the "Detroit No-Spin," which replaces the entire differential carrier assembly.

Jonathan

 

Edited by - Jonathan Kay on 3 Apr 2014 13:47:22

[tony pashley]

Ok - thanks Jonathan; I'd skipped over that ref 'cause I thought an automatic locker was something else. 'A little knowledge' and all that...!

[Jonathan Kay]

:-)

 

I'm intrigued by the 980, 917 etc. I remember that vaguely (and saw lots of both racing) but I'm trying to work out what the issues would have been at that sort of power:mass ratio. Were they prepared to spin a tyre up in many corners?

 

Jonathan

[tony pashley]

The 917 - the Group 5 coupe version - had a ZF lsd which, according to one of Paul Frere's books, was "preloaded and with a 75% locking factor".

 

The later CanAm versions ended up with a solid rear end, but they were essentially developed by Donohue and Penske rather than Porsche.

 

I don't know about the 908s but they were much less brutal machines altogether, so I also don't understand what that would achieve. (It's hard to imagine 908/3, at least, having a locked diff as that was built for events like the Targa Florio, which doesn't sound like a suitable arrangement.)